CN109985663B

CN109985663B - Method for post-treating Cu-SSZ-13 molecular sieve synthesized in situ by one-pot method

Info

Publication number: CN109985663B
Application number: CN201711484186.2A
Authority: CN
Inventors: 李涛; 范驰; 陈真
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2020-09-08
Anticipated expiration: 2037-12-29
Also published as: CN109985663A

Abstract

The invention belongs to the field of chemistry, and provides a method for post-treating a Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method, which comprises the steps of adding the Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method into an alkali solution with the pH value of 7-10, stirring for 2-24 hours at the temperature of 25-80 ℃, washing, filtering and drying to obtain a Cu-SSZ-13 catalyst. The catalyst prepared by the method has excellent low-temperature activity, excellent hydrothermal stability and excellent metal poisoning resistance, can adapt to complex and harsh working conditions in a diesel vehicle aftertreatment system, and can be used for selectively catalytically reducing Nitrogen Oxides (NO) through ammonia gas in the diesel vehicle aftertreatment system_x) To purify the tail gas NO of the diesel vehicle_xThe object of (a); the alkalescent solution is used, so the method has low requirements on reaction equipment, convenient and easily obtained raw materials of sodium hydroxide or potassium hydroxide, low cost, convenient storage and transportation, safe operation and suitability for large-scale industrial production.

Description

Method for post-treating Cu-SSZ-13 molecular sieve synthesized in situ by one-pot method

Technical Field

The invention belongs to the field of chemistry, relates to a preparation method of a Cu-SSZ-13catalyst, and particularly relates to a method for preparing the Cu-SSZ-13catalyst by carrying out post-treatment on a Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method.

Background

Nitrogen Oxides (NO)_x) As pollutants in industrial production and in motor vehicle exhaust, are the cause of photochemical smog, acid rain and haze. To meet increasingly stringent emission standards, NH₃The SCR technology is widely used in exhaust gas purification of diesel vehicles.

V₂O₅-WO₃(MoO₃)/TiO₂The catalyst is also introduced into the purification of exhaust gas from diesel vehicles as a commonly used fixed source denitration catalyst. However, the catalyst has a narrow temperature window (300-₂Oxidizing property and V₂O₅The wide range of applications is limited by the biotoxicity of (a). While other molecular sieve type catalysts such as Cu-ZSM-5, Cu-BEA and Cu-Y, although they are very environment friendly, their poor hydrothermal stability, metal poisoning resistance and HC poisoning resistance also limit their application in diesel vehicle exhaust gas purification.

Cu-SSZ-13 as a small pore molecular sieveThe maximum aperture is only 0.38nm, the high-temperature dealumination phenomenon can be effectively inhibited, and the N is good₂And (4) selectivity. In addition, Cu-SSZ-13 can inhibit the generation of carbon deposit and exhibit strong poisoning resistance to metals, and thus has received much attention and is recognized as the next generation NH₃-an SCR catalyst. The preparation method of the Cu-SSZ-13catalyst mainly comprises two methods, wherein one method comprises the steps of firstly synthesizing an SSZ-13 carrier and then loading Cu species on the carrier by an exchange method. The method uses expensive organic template agent N, N, N-trimethyl adamantine ammonium hydroxide, and greatly improves the industrial production cost. The ion exchange process in the preparation process consumes a large amount of distilled water and has complicated steps, and the SSZ-13 carriers with different Si/Al ratios have different Cu exchange degrees, thereby bringing great inconvenience to large-scale production. The other preparation method is to use a Cu-TEPA complex as a template agent to synthesize the Cu-SSZ-13catalyst in situ by a one-pot method. The template agent used by the method is cheap and easy to obtain, the preparation process is simple, and the method is very beneficial to the industrial production of the catalyst. However, the Cu content of the synthesized catalyst is high, which causes the reduction of the hydrothermal stability of the catalyst and NH at a high temperature section₃The oxidation of (2) thus requires a suitable post-treatment of the in-situ synthesized Cu-SSZ-13 in order to achieve the reduction of the Cu content. Currently, ammonium nitrate exchange is a common post-treatment process, which utilizes NH₄ ⁺Ions with Cu²⁺Exchange is carried out to achieve the purpose of reducing the Cu content. Although the method is simple and effective, the ammonium nitrate belongs to controlled medicines, and the production, transportation and use of the ammonium nitrate are greatly limited. Hehong (Hehong, Xiliejuan, etc., a Cu-SSZ-13catalyst, a preparation method and its use, CN103157505A) utilizes acid as an exchanger to post-treat Cu-SSZ-13 synthesized in situ, and obtains a catalyst with high freshness activity and hydrothermal stability. However, the nitric acid, the sulfuric acid and the hydrochloric acid in the report belong to strong acids, have strong oxidizability, corrosiveness or irritation, bring many potential safety hazards in the processes of transportation, storage and use, and have high requirements on treatment equipment. The solution needs to be heated to 80 ℃ in the post-treatment process, the volatilization of acid is easily caused, the production cost is increased, andenvironmental pollution and is not beneficial to large-scale industrial production. Therefore, the Cu-SSZ-13catalyst with excellent activity is prepared by using a more environment-friendly and safer post-treatment method, and the large-scale production and application of the Cu-SSZ-13catalyst are facilitated.

Disclosure of Invention

The invention aims to provide a method for post-treating a Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method so as to prepare a Cu-SSZ-13 catalyst.

The specific technical scheme for realizing the invention is as follows:

the invention provides a post-treatment method for a Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method, which comprises the following steps: adding a Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method into an alkaline solution with the pH value of 7-10, stirring for 2-24 hours at the temperature of 25-80 ℃, washing, filtering and drying to obtain a Cu-SSZ-13catalyst, wherein the alkali is selected from any one or a mixture of at least two of sodium hydroxide, potassium hydroxide, ammonia water, triethylamine and diethylamine, the pH value of the alkaline solution is 7-10, specifically 7.2, 7.5, 8.2, 8.6, 8.9, 9.2, 9.5 or 10, and preferably the pH value is 9; the stirring time is preferably 8 to 16 hours, and more preferably 12 hours. In one embodiment of the invention, the stirring is performed at 25 ℃ for 12 hours; the specific method for washing, filtering and drying can be as follows: washing with distilled water for 3 times, filtering, and drying at 100 deg.C for 12 hr.

The Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method can be used for the selective catalytic reduction process of nitrogen oxides in tail gas of diesel vehicles by the Cu-SSZ-13catalyst prepared by the post-treatment method provided by the invention.

The method for post-treating the Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method has simple treatment steps, avoids the use of ammonium nitrate and strong acid, does not need to heat the solution, and reduces the cost. The Cu-SSZ-13catalyst obtained by the post-treatment method has excellent low-temperature catalytic activity and hydrothermal stability, shows good metal poisoning resistance, and can be used for mobile source denitration, such as the selective catalytic reduction process of nitrogen oxides in diesel vehicle tail gas.

The one-pot in situ synthesis of Cu-SSZ-13 is a prior art, such as the method disclosed in the paper published by Tao Li in 2017 (Tao Li, Stem and alkali reactive Cu-SSZ-13catalyst for the selective catalytic reduction of NO)_xin diesel exhaust, chem. eng.j.334(2018) 344-354). The initial Cu-SSZ-13catalyst prepared by the method has higher Cu content and is not beneficial to NH₃SCR reaction, therefore it is necessary to carry out a suitable aftertreatment of the Cu-SSZ-13 to prepare a catalyst with a moderate Cu content. The method adopts the alkaline solution, has no volatilization and does not need heating, overcomes the problems of environmental pollution caused by the existing ammonium nitrate exchange method and acid exchange method and the potential safety hazard in the process of using the exchanger, and the catalyst after the alkaline treatment has better low-temperature catalytic activity.

The alkali liquor is used as a treating agent, so that the molecular sieve can be desiliconized, mesopores can be generated, and the low-temperature activity of the catalyst can be effectively improved while the structural integrity of the molecular sieve is maintained. The low-temperature activity is a key factor of the low-temperature working condition of the diesel vehicle WHTC test cycle meeting the national VI emission regulations, so the alkaline solution treatment method has the potential as a novel post-treatment method.

Compared with the prior art, the invention has the following advantages: (1) the catalyst prepared by the post-treatment method provided by the invention has excellent low-temperature activity and can meet the emission requirement of the latest regulation on the low-temperature cold start of the catalyst; (2) the catalyst prepared by the post-treatment method provided by the invention has the advantages that the Cu content is reduced, the structure of the catalyst is not damaged, and the integrity of the framework structure of the catalyst is ensured, so that the catalyst has excellent hydrothermal stability; (3) the catalyst prepared by the post-treatment method provided by the invention still can show excellent NO after metal poisoning_xThe conversion rate proves that the catalyst has excellent metal poisoning resistance and can adapt to complex and harsh working conditions in a diesel vehicle aftertreatment system; (4) the post-treatment method provided by the invention uses weak alkaline solution, has lower requirements on reaction equipment, is convenient and easy to obtain raw material sodium hydroxide or potassium hydroxide, has low cost, convenient storage and transportation, and is safe and invisible in operationPatients suffer from it. The operation is simple in the treatment process, the solution does not need to be heated, the energy consumption can be saved, the cost is reduced, and the method is very favorable for large-scale industrial production. The Cu-SSZ-13catalyst prepared by the post-treatment method provided by the invention can generate mesopores, reduce low-temperature diffusion inhibition, effectively improve the low-temperature activity of the catalyst, and can still reach more than 85 percent of NO at the temperature of 175-_xAnd (4) conversion rate. In addition, the framework structure of the catalyst subjected to alkali treatment is not obviously damaged, and the hydrothermal stability of the catalyst can be well maintained.

Drawings

FIG. 1 is a comparison of fresh activity and 750 ℃ aging hydrothermal stability of a Cu-SSZ-13catalyst (Cu-2) prepared by the method of the present invention and a Cu-SSZ-13catalyst (Cu-1) obtained by a conventional ammonium nitrate exchange treatment in example 1 of the present invention, wherein a mark Cu-2 indicates the Cu-SSZ-13catalyst prepared by the post-treatment method of the present invention; the designation Cu-1 in the figure shows the Cu-SSZ-13catalyst obtained with a conventional ammonium nitrate exchange treatment.

FIG. 2 is a line chart showing the metal (K, Ca, Na, Mg) poisoning resistance of the Cu-SSZ-13catalyst (Cu-2) prepared by the method of the present invention in example 1 of the present invention.

Detailed Description

The technical solution of the present invention will be further described with reference to the following embodiments.

Example 1

The method provided by the invention is adopted to carry out post-treatment on the Cu-SSZ-13 molecular sieve synthesized in situ by a one-pot method to prepare the Cu-SSZ-13 catalyst:

preparing a sodium hydroxide solution with the pH of 9, adding a Cu-SSZ-13 molecular sieve which is calcined at the temperature of 600 ℃ and synthesized in situ by a one-pot method into the sodium hydroxide solution, stirring for 12 hours at the room temperature of 25 ℃, washing for 3 times by using distilled water, and finally drying for 12 hours at the temperature of 100 ℃ to obtain the final Cu-SSZ-13 catalyst.

Example 2

The Cu-SSZ-13catalyst was evaluated by the following method:

2g of the catalyst powder was mixed with an appropriate amount of water to prepare a slurry and applied to cordieriteThe coating amount of the slurry prepared by the catalyst powder is about 250 g.L^-1Drying a sample at 100 ℃ for 2 hours to obtain the prepared integral Cu-LTA catalyst, putting the integral Cu-LTA catalyst into a fixed bed activity evaluation device, and simulating the smoke with the composition of 1000ppm NO and 1100ppm NH₃,5％O₂And 10% of H₂O, the reaction space velocity is 30,000h^-1。

The hydrothermal aging of the catalyst adopts the following method:

the monolithic catalyst was placed in an aging apparatus, heated to 750 ℃ at a rate of 10 ℃/min, and air and 10% steam were introduced and maintained at this temperature for 12 hours.

The metal poisoning of the catalyst adopts the following method:

and respectively putting the catalyst (Cu-2) obtained by treating the prepared alkali solution into potassium nitrate, calcium nitrate, sodium nitrate and magnesium nitrate solutions with certain concentrations, and loading metal on the catalyst by adopting an immersion method, wherein the metal loading is 0.50 mmol/catalyst. The conversion of the catalyst Cu-SSZ-13 (Cu-1) obtained by conventional ammonium nitrate treatment and the catalyst Cu-2 obtained by alkali treatment in example 1 after hydrothermal aging at 750 ℃ is shown in FIG. 1, and the conversion of the catalyst subjected to metal poisoning is shown in FIG. 2. As can be seen from FIG. 1, the base treated catalyst (Cu-2) exhibited better low temperature (175-_xAnd (4) conversion rate. Meanwhile, after hydrothermal aging at 750 ℃, the catalyst (Cu-2) obtained by the alkali treatment in example 1 still showed excellent hydrothermal stability, which indicates that the alkali treatment did not substantially damage the catalyst structure. As can be seen from FIG. 2, the base treated catalyst (Cu-2) of example 1 still exhibited high NO after metal poisoning_xThe conversion rate shows that the catalyst has excellent metal poisoning resistance.

In conclusion, the Cu-SSZ-13catalyst after the alkali treatment has excellent fresh activity, hydrothermal stability and metal poisoning resistance, can adapt to complex and harsh working conditions in the diesel vehicle aftertreatment, and is very suitable for purifying nitrogen oxides in the diesel vehicle exhaust.

The applicant declares that any modification of the present invention, equivalent substitution of the raw materials of the product of the present invention and addition of auxiliary components, selection of specific modes and the like, which are obvious to a person skilled in the art, fall within the protection scope and disclosure of the present invention.

Claims

1. The application of the alkali solution in reducing the Cu content of the Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method and improving the catalytic activity of the Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method is characterized in that the application is specifically that the Cu-SSZ-13 molecular sieve synthesized in situ by the one-pot method is added into the alkali solution with the pH value of 7-10, stirred for 2-24 hours at the temperature of 25-80 ℃, washed, filtered and dried to obtain the Cu-SSZ-13catalyst, and the alkali is selected from any one or a mixture of at least two of sodium hydroxide, potassium hydroxide, ammonia water, triethylamine and diethylamine.

2. Use according to claim 1, wherein the alkaline solution has a pH of 9.

3. Use according to claim 1, wherein the stirring time is 8 to 16 hours.

4. Use according to claim 1, wherein the stirring is carried out at 25 ℃ for 12 hours.

5. The application of claim 1, wherein the specific methods of washing, filtering and drying are as follows: washed with distilled water 3 times, filtered, and then dried at 100 ℃ for 12 hours.